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@Article { ZaretskayaFRRP2017,
title = {Advantages of cortical surface reconstruction using submillimeter 7 T MEMPRAGE},
journal = {NeuroImage},
year = {2018},
month = {1},
volume = {165},
pages = {11-26},
abstract = {Recent advances in MR technology have enabled increased spatial resolution for routine functional and anatomical imaging, which has created demand for software tools that are able to process these data. The availability of high-resolution data also raises the question of whether higher resolution leads to substantial gains in accuracy of quantitative morphometric neuroimaging procedures, in particular the cortical surface reconstruction and cortical thickness estimation. In this study we adapted the FreeSurfer cortical surface reconstruction pipeline to process structural data at native submillimeter resolution. We then quantified the differences in surface placement between meshes generated from (0.75 mm)3 isotropic resolution data acquired in 39 volunteers and the same data downsampled to the conventional 1 mm3 voxel size. We find that when processed at native resolution, cortex is estimated to be thinner in most areas, but thicker around the Cingulate and the Calcarine sulci as well as in the posterior bank of the Central sulcus. Thickness differences are driven by two kinds of effects. First, the gray–white surface is found closer to the white matter, especially in cortical areas with high myelin content, and thus low contrast, such as the Calcarine and the Central sulci, causing local increases in thickness estimates. Second, the gray–CSF surface is placed more interiorly, especially in the deep sulci, contributing to local decreases in thickness estimates. We suggest that both effects are due to reduced partial volume effects at higher spatial resolution. Submillimeter voxel sizes can therefore provide improved accuracy for measuring cortical thickness.},
department = {Department Logothetis},
department2 = {Department Scheffler},
web_url = {http://www.sciencedirect.com/science/article/pii/S105381191730808X},
DOI = {10.1016/j.neuroimage.2017.09.060},
author = {Zaretskaya, N and Fischl, B and Reuter, M and Renvall, V and Polimeni, JR}
}
@Article { MolaeiVaneghiZSB2018,
title = {9.4T Human fMRI Study Reveals that Real World Motion Perception Does Not Involve Laminar Organization in V1 and V5/MT},
journal = {-},
year = {2018},
month = {1},
department = {Department Scheffler},
department2 = {Department Logothetis},
state = {in_preparation},
author = {Molaei-Vaneghi, F and Zaretskaya, N and Scheffler, K and Bartels, A}
}
@Article { MolaeiVaneghiZVSB2018,
title = {Perception of Real World Motion in V6 is Mediated by Integration between Feedforward Retinal Inputs and Feedback Efference Copies of Eye movement: A 9.4T Human fMRI Study},
journal = {-},
year = {2018},
month = {1},
department = {Department Scheffler},
department2 = {Department Logothetis},
state = {in_preparation},
author = {Molaei-Vaneghi, F and Zaretskaya, N and Van Mourik, T and Scheffler, K and Bartels, A}
}
@Article { JusyteZHBS2017,
title = {Binocular rivalry transitions predict inattention symptom severity in adult ADHD},
journal = {European Archives of Psychiatry and Clinical Neuroscience},
year = {2017},
month = {4},
volume = {Epub ahead},
abstract = {Attention deficit and hyperactivity disorder (ADHD) is a prevalent childhood disorder that is often maintained throughout the development and persists into adulthood. Established etiology models suggest that deficient inhibition underlies the core ADHD symptoms. While experimental evidence for impaired motor inhibition is overwhelming, little is known about the sensory inhibition processes, their changes throughout the development, and the relationship to ADHD symptoms. Here, we used the well-established binocular rivalry (BR) paradigm to investigate for the very first time the inhibitory processes related to visual perception in adults with ADHD. In BR, perception alternates between two dichoptically presented images throughout the viewing period, with shorter dominant percept durations and longer transition periods indicating poorer suppression/inhibition. Healthy controls (N = 28) and patients with ADHD (N = 32) were presented with two dissimilar images (orthogonal gratings) separately to each eye through a mirror stereoscope and asked to report their perceptual experiences. There were no differences between groups in any of the BR markers. However, an association between transition durations and symptom severity emerged in the ADHD group. Importantly, an exploratory multiple regression analysis revealed that inattention symptoms were the sole predictor for the duration of transition periods. The lack of impairments to sensory inhibition in adult, but not pediatric ADHD may reflect compensatory changes associated with development, while a correlation between inhibition and inattention symptoms may reveal an invariant core of the disorder.},
department = {Department Logothetis},
web_url = {http://link.springer.com/content/pdf/10.1007\%2Fs00406-017-0790-1.pdf},
DOI = {10.1007/s00406-017-0790-1},
author = {Jusyte, A and Zaretskaya, N and H{\"o}hnle, NM and Bartels, A and Sch{\"o}nenberg, M}
}
@Article { PolimeniRZF2017,
title = {Analysis strategies for high-resolution UHF-fMRI data},
journal = {NeuroImage},
year = {2017},
month = {4},
volume = {Epub ahead},
abstract = {Functional MRI (fMRI) benefits from both increased sensitivity and specificity with increasing magnetic field strength, making it a key application for Ultra-High Field (UHF) MRI scanners. Most UHF-fMRI studies utilize the dramatic increases in sensitivity and specificity to acquire high-resolution data reaching sub-millimeter scales, which enable new classes of experiments to probe the functional organization of the human brain. This review article surveys advanced data analysis strategies developed for high-resolution fMRI at UHF. These include strategies designed to mitigate distortion and artifacts associated with higher fields in ways that attempt to preserve spatial resolution of the fMRI data, as well as recently introduced analysis techniques that are enabled by these extremely high-resolution data. Particular focus is placed on anatomically-informed analyses, including cortical surface-based analysis, which are powerful techniques that can guide each step of the analysis from preprocessing to statistical analysis to interpretation and visualization. New intracortical analysis techniques for laminar and columnar fMRI are also reviewed and discussed. Prospects for single-subject individualized analyses are also presented and discussed. Altogether, there are both specific challenges and opportunities presented by UHF-fMRI, and the use of proper analysis strategies can help these valuable data reach their full potential.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science/article/pii/S1053811917303713},
state = {},
DOI = {10.1016/j.neuroimage.2017.04.053},
author = {Polimeni, JR and Renvall, V and Zaretskaya, N and Fischl, B}
}
@Article { GrassiZB2016_5,
title = {Scene segmentation in early visual cortex during suppression of ventral stream regions},
journal = {NeuroImage},
year = {2017},
month = {2},
volume = {146},
pages = {71–80},
abstract = {A growing body of literature suggests that feedback modulation of early visual processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content that invariably activate ventral object responsive regions have been shown to suppress early visual cortex. This suppression was typically interpreted in the framework of predictive coding and feedback from ventral regions. Here we examined early visual modulation during perception of a bistable Gestalt illusion that has previously been shown to be mediated by dorsal parietal cortex rather than by ventral regions that were not activated. The bistable dynamic stimulus consisted of moving dots that could either be perceived as corners of a large moving cube (global Gestalt) or as distributed sets of locally moving elements. We found that perceptual binding of local moving elements into an illusory Gestalt led to spatially segregated differential modulations in both, V1 and V2: representations of illusory lines and foreground were enhanced, while inducers and background were suppressed. Furthermore, correlation analyses suggest that distinct mechanisms govern fore- and background modulation. Our results demonstrate that motion-induced Gestalt perception differentially modulates early visual cortex in the absence of ventral stream activation.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science/article/pii/S1053811916306437},
DOI = {10.1016/j.neuroimage.2016.11.024},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Article { GrassiZB2016,
title = {Parietal cortex mediates perceptual Gestalt grouping independent of stimulus size},
journal = {NeuroImage},
year = {2016},
month = {6},
volume = {133},
pages = {367–377},
abstract = {The integration of local moving elements into a unified gestalt percept has previously been linked to the posterior parietal cortex. There are two possible interpretations for the lack of involvement of other occipital regions. The first is that parietal cortex is indeed uniquely functionally specialized to perform grouping. Another possibility is that other visual regions can perform grouping as well, but that the large spatial separation of the local elements used previously exceeded their neurons' receptive field (RF) sizes, preventing their involvement. In this study we distinguished between these two alternatives. We measured whole-brain activity using fMRI in response to a bistable motion illusion that induced mutually exclusive percepts of either an illusory global Gestalt or of local elements. The stimulus was presented in two sizes, a large version known to activate IPS only, and a version sufficiently small to fit into the RFs of mid-level dorsal regions such as V5/MT. We found that none of the separately localized motion regions apart from parietal cortex showed a preference for global Gestalt perception, even for the smaller version of the stimulus. This outcome suggests that grouping-by-motion is mediated by a specialized size-invariant mechanism with parietal cortex as its anatomical substrate.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science/article/pii/S1053811916002044},
DOI = {10.1016/j.neuroimage.2016.03.008},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Article { ZaretskayaB2015,
title = {Gestalt perception is associated with reduced parietal beta oscillations},
journal = {NeuroImage},
year = {2015},
month = {5},
volume = {112},
pages = {61–69},
abstract = {The ability to perceive composite objects as a whole is fundamental for visual perception in a complex and cluttered natural environment. This ability may be mediated by increased communication between neural representations of distinct object elements, and has been linked to increased synchronization of oscillatory brain activity in the gamma band. Previous studies of perceptual grouping either guided attention between local and global aspects of a given stimulus or manipulated its physical properties to achieve grouped and ungrouped perceptual conditions. In contrast to those studies, we fully matched the physical properties underlying global and local percepts using a bistable stimulus that causes the viewer to perceive either local motion of multiple elements or global motion of two illusory shapes without any external change. To test the synchronization hypothesis we recorded brain activity with EEG, while human participants viewed the stimulus and reported changes in their perception. In contrast to previous findings we show that power of the beta-band was lower during perception of global Gestalt than during that of local elements. Source localization places these differences in the posterior parietal cortex, overlapping with a site previously associated with both attention and Gestalt perception. These findings reveal a role of parietal beta-band activity in internally, rather than externally or attention-driven processes of Gestalt perception. They also add to the growing evidence for shared neural substrates of attention and Gestalt perception, both being linked to parietal cortex.},
web_url = {http://www.sciencedirect.com/science/article/pii/S1053811915001500},
DOI = {10.1016/j.neuroimage.2015.02.049},
author = {Zaretskaya, N and Bartels, A}
}
@Article { ZaretskayaN2014,
title = {Introspection, attention or awareness? The role of the frontal lobe in binocular rivalry},
journal = {Frontiers in Human Neuroscience},
year = {2014},
month = {7},
volume = {8},
number = {527},
pages = {1-2},
abstract = {Bistable stimuli are one of the most popular approaches to studying the neural mechanism of conscious visual perception. Such stimuli contain conflicting information, which the visual system cannot integrate into a unified percept. This causes the perceptual state of the observer to change every few seconds between the two interpretations while the physical stimulus remains the same. Binocular rivalry is an example of such perceptual phenomena with ambiguity achieved by presenting one image to one eye and a different image to the other eye. Perceptual changes during binocular rivalry are particularly vivid, and closely resemble a physical image exchange.},
department = {Department Logothetis},
web_url = {http://journal.frontiersin.org/Journal/10.3389/fnhum.2014.00527/pdf},
DOI = {10.3389/fnhum.2014.00527},
author = {Zaretskaya, N and Narinyan, M}
}
@Article { ZaretskayaB2013,
title = {Perceptual effects of stimulating V5/hMT+ during binocular rivalry are state specific},
journal = {Current Biology},
year = {2013},
month = {10},
volume = {23},
number = {20},
pages = {R919-R920},
abstract = {Binocular rivalry occurs when two distinct visual stimuli are presented separately to each eye, causing perceptual ambiguity. The conscious state of the observer then alternates between the perceptual dominance of one of the stimuli while the other is suppressed, and vice versa. These vivid changes in perception during constant visual stimulation allow the study of brain processes involved in conscious visual experience. There is abundant electrophysiological as well as fMRI evidence that neural activity in stimulus-selective areas of the temporal lobe correlates with perceptual changes during rivalry [1,2,3]. Yet, almost nothing is known about the causal contribution of these areas to dominance and suppression of their preferred stimulus. We induced binocular rivalry in human observers using moving dots presented to one eye and a static face to the other eye, and applied transcranial magnetic stimulation (TMS) over the motion area V5/hMT+. We show that disrupting activity in V5/hMT+ during rivalry extends periods of motion suppression, with no effect on periods of motion dominance, revealing a state-specific contribution of V5/hMT+ to the competition for awareness in rivalry.},
department = {Department Logothetis},
web_url = {http://download.cell.com/current-biology/pdf/PIIS0960982213011093.pdf},
DOI = {10.1016/j.cub.2013.09.002},
author = {Zaretskaya, N and Bartels, A}
}
@Article { ZaretskayaAB2012,
title = {Parietal Cortex Mediates Conscious Perception of Illusory Gestalt},
journal = {Journal of Neuroscience},
year = {2013},
month = {1},
volume = {33},
number = {2},
pages = {523-531},
abstract = {Grouping local elements into a holistic percept, also known as spatial binding, is crucial for meaningful perception. Previous studies have shown that neurons in early visual areas V1 and V2 can signal complex grouping-related information, such as illusory contours or object-border ownerships. However, relatively little is known about higher-level processes contributing to these signals and mediating global Gestalt perception. We used a novel bistable motion illusion that induced alternating and mutually exclusive vivid conscious experiences of either dynamic illusory contours forming a global Gestalt or moving ungrouped local elements while the visual stimulation remained the same. fMRI in healthy human volunteers revealed that activity fluctuations in two sites of the parietal cortex, the superior parietal lobe and the anterior intraparietal sulcus (aIPS), correlated specifically with the perception of the grouped illusory Gestalt as opposed to perception of ungrouped local elements. We then disturbed activity at these two sites in the same participants using transcranial magnetic stimulation (TMS). TMS over aIPS led to a selective shortening of the duration of the global Gestalt percept, with no effect on that of local elements. The results suggest that aIPS activity is directly involved in the process of spatial binding during effortless viewing in the healthy brain. Conscious perception of global Gestalt is therefore associated with aIPS function, similar to attention and perceptual selection.},
department = {Department Logothetis},
web_url = {http://www.jneurosci.org/content/33/2/523.full.pdf+html},
DOI = {10.1523/​JNEUROSCI.2905-12.2013},
author = {Zaretskaya, N and Anstis, S and Bartels, A}
}
@Article { 6902,
title = {Disrupting Parietal Function Prolongs Dominance Durations in Binocular Rivalry},
journal = {Current Biology},
year = {2010},
month = {12},
volume = {20},
number = {23},
pages = {2106-2111},
abstract = {Human brain imaging studies of bistable perceptual phenomena revealed that frontal and parietal areas are activated during perceptual switches between the two conflicting percepts [1,2,3]. However, these studies do not provide information about causality, i.e., whether activity reports a consequence or a cause of the perceptual change. Here we used functional magnetic resonance imaging to individually localize four parietal regions involved in perceptual switches during binocular rivalry in 15 subjects and subsequently disturbed their neural processing and that of a control site using 2 Hz repetitive transcranial magnetic stimulation (TMS) during binocular rivalry. We found that TMS over one of the sites, the right intraparietal sulcus (IPS), prolonged the periods of stable percepts. Additionally, the more lateralized the blood oxygen level-dependent signal was in IPS, the more lateralized the TMS effects were. Lateralization varied considerably across subjects, with a right-hemispheric bias. Control replay e
xperiments rule out nonspecific effects of TMS on task performance, reaction times, or eye blinks. Our results thus demonstrate a causal, destabilizing, and individually lateralized effect of normal IPS function on perceptual continuity in rivalry. This is in accord with a role of IPS in perceptual selection, relating its role in rivalrous perception to that in attention [4,5,6].},
department = {Department Logothetis},
department2 = {Department MRZ},
web_url = {http://www.sciencedirect.com/science/article/pii/S0960982210013618},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.cub.2010.10.046},
author = {Zaretskaya, N and Thielscher, A and Logothetis, NK and Bartels, A}
}
@Poster { ZaretskayaBPSB2017,
title = {Detecting eye-selective fMRI activity in the human primary visual cortex at 3T and 9.4T},
year = {2017},
month = {11},
day = {14},
abstract = {Introduction
The primary visual cortex of humans contains patches of neurons responding preferentially to stimulation of one eye (ocular dominance columns) (Adams et al., 2007). The majority of previous fMRI studies reporting eye-specific activity in V1 used magnetic field strengths of 4 T and higher (Cheng et al., 2001; Yacoub et al., 2007; Nasr et al., 2016). However, there have been reports of reliable eye-selective activations at 3 T (Haynes et al., 2005). Here we present preliminary results on the ability to detect eye-selective V1 activity using high-resolution fMRI at 3 T and 9.4 T.
Methods
BOLD signal of one healthy adult volunteer was measured at 3 T and 9.4 T using 2D GE-EPI (3 T: 1.5mm isotropic resolution, TR/TE/matrix/GRAPPA = 1720/30/128x128x24/R=3, 873 volumes; 9.4 T: 0.8mm isotropic resolution TR / TE / matrix / GRAPPA=2 s / 22 ms /230\(\times\)230\(\times\)40 / R=5, FLEET autocalibration (Polimeni et al., 2016), 900 volumes). Each eye was stimulated separately with a checkerboard flickering at 2 Hz for 18 s with 18 s breaks, viewed through a prism stereo display (Schurger, 2009). Structural scans (1mm3 for 3 T and 0.6 mm3 for 9.4 T) were acquired in each session for cortical surface reconstruction.
All analyses were performed using FreeSurfer 6.0 and FS-FAST (Fischl, 2012). Functional data were motion-corrected, co-registered to the anatomy using boundary-based registration (Greve and Fischl, 2009) with 6 DOF for 3 T and 9 DOF locally constrained to V1 for 9.4 T, and analyzed using voxel-wise GLM with left eye, right eye and baseline regressors. Surface-based prediction of V1 location (Hinds et al., 2008) was used to label volume voxels belonging to V1 gray matter, and z-statistics of the contrast “left eye vs. right eye” were extracted from those voxels.
Results
We observed a more than two-fold increase in the percentage of eye-selective voxels and in run-to-run correlation of eye preference at ultrahigh field.
Conclusion
Increase in spatial resolution and improved BOLD point spread function at 9.4T allows for better detection of eye-selective signal related to ocular dominance columns.},
department = {Department Scheffler},
department2 = {Department Logothetis},
web_url = {http://www.abstractsonline.com/pp8/\#!/4376/presentation/18809},
event_place = {Washington, DC, USA},
event_name = {47th Annual Meeting of the Society for Neuroscience (Neuroscience 2017)},
author = {Zaretskaya, N and Bause, J and Polimeni, JR and Scheffler, K and Bartels, A}
}
@Poster { JusyteZHBS2017_2,
title = {Binocular rivalry transitions predict inattention symptom severity in adult ADHD},
year = {2017},
month = {8},
day = {29},
department = {Department Logothetis},
web_url = {http://www.ecvp.org/2017/programme.html},
event_place = {Berlin, Germany},
event_name = {40th European Conference on Visual Perception (ECVP 2017)},
author = {Jusyte, A and Zaretskaya, N and H{\"o}hnle, NM and Bartels, A and Sch{\"o}nenberg, M}
}
@Poster { GrassiZB2017_2,
title = {A generic mechanism for perceptual organisation in the parietal cortex},
year = {2017},
month = {8},
day = {28},
department = {Department Logothetis},
web_url = {http://www.ecvp.org/2017/programme.html},
event_place = {Berlin, Germany},
event_name = {40th European Conference on Visual Perception (ECVP 2017)},
author = {Grassi, P and Zaretskaya, N and Bartels, A}
}
@Poster { PolimeniZSBEWS2017,
title = {Macrovascular contributions to high-resolution balanced SSFP- and GE-EPI-based fMRI at 9.4T evaluated using surface-based cortical depth analyses in human visual cortex},
year = {2017},
month = {4},
day = {27},
number = {5255},
abstract = {Several strategies have been proposed for maximizing neuronal specificity of fMRI by utilizing pulse sequences that are primarily sensitive to signal changes within microvasculature. Here we compare the microvascular sensitivity of high-resolution balanced SSFP and gradient-echo EPI at 9.4T using cortical depth analyses within human visual cortex. Because of the large draining vessels lying along the pial surface, the behavior of fMRI signals as a function of cortical depth can provide helpful insights into the vascular contributions. Our preliminary analyses suggest that, for the protocols used here, both balanced SSFP and EPI show similar cortical depth profiles of BOLD responses.},
department = {Department Scheffler},
web_url = {http://www.ismrm.org/17/program_files/EP17.htm},
event_place = {Honolulu, HI, USA},
event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)},
author = {Polimeni, J and Zaretskaya, N and Stelzer, J and Bause, J and Ehses, P and Wald, L and Scheffler, K}
}
@Poster { GrassiZB2017,
title = {Retinotopic specific modulations in early visual cortex
by feedback during bistable Gestalt perception},
year = {2017},
month = {3},
pages = {25},
abstract = {A growing body of literature suggests that feedback modulation of early visual processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content have been shown to suppress early visual regions, typically interpreted in the framework of predictive coding. However, physical stimulus differences can preclude clear interpretations in terms of feedback.
Here we examined activity modulation in V1 and V2 during distinct perceptual states associated to the same physical input. This ensures in a unique way that observed signal modulations cannot be accounted for by changes in physical stimulus properties, and can therefore only be accounted for by percept-related feedback interactions from higher level regions.
We used a dynamic stimulus consisting of moving dots that could either be perceived as corners of a large moving square (global Gestalt) or as distributed sets of locally moving dots. We found that perceptual binding of local moving elements into an illusory Gestalt led to spatially segregated differential modulations, in both, V1 and V2: representations of illusory lines and foreground were
enhanced, while inducers and background suppressed. The results extend prior findings to the illusory-perceptual state of physically un- ‐changed stimuli, and for the first time show background suppression in the human brain.
Based on prior work (Zaretskaya et al., 2013), we hypothesize that parietal cortex is responsible for the
modulations through recurrent connections in a predictive coding account of visual processing.},
department = {Department Logothetis},
web_url = {http://www.cogsci.uni-jena.de/wa_files/CombinedPages2.pdf},
event_place = {Jena, Germany},
event_name = {Cortical Feedback Springschool (COFEES 2017)},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Poster { GrassiZB2016_4,
title = {A generic mechanism for Gestalt and high-level stimulus interpretation in the human brain},
year = {2016},
month = {11},
day = {14},
number = {360.02},
abstract = {A common denominator in all vision tasks is scene segmentation: what is fore- and background, which visual components belong to the same or different entities? In prior studies we used a bi-stable stimulus that can either be perceived as separate local components or as a global Gestalt. fMRI and TMS showed that posterior parietal cortex (PPC) was selectively and causally involved in global Gestalt perception (Grassi et al., 2016; Zaretskaya et al., 2013).
Here we employed three additional such local vs. global bi-stable stimuli. Importantly, we found that apart from the classification of the two possible percepts into local (ungrouped, component) versus global (grouped, Gestalt), the two possible perceptual interpretations can alternatively be classified according to a second dimension: the complexity or sophistication of the interpretation, i.e. default (simple) versus non-default (complex, high-level, sophisticated). As these two dimensions overlapped differentially across the four stimulus classes (for two stimuli, global coincided with complex, in another two with simple), we were able to identify whether parietal cortex involvement reflected grouping, or the complexity of the perceptual interpretation.
We found that the involvement of parietal cortex reflected the level of sophistication of the visual interpretation rather than grouping into a single Gestalt. For all four stimuli, we found activity pattern that was highly similar for the contrast of default (simple) vs. non-default (complex, sophisticated) perceptual interpretations. It consistently and prominently involved posterior parietal cortex. Also consistent with previous findings, we found for all stimuli strong early visual cortex deactivations during sophisticated perceptual interpretations. Mid-level regions such as LOC or motion regions were differentially involved with each stimulus class and percept-type. Our results lead us to suggest that PPC is not necessarily involved in mere grouping toward global Gestalt, but instead more generally it is involved in generating the more complex, high-level, or more sophisticated perceptual interpretation of a given stimulus. The activation of high-level dorsal areas (PPC) and the concurrent deactivation of early visual areas during high-level perceptual interpretations is in line with predictions from generative models of visual perception, also known as predictive coding theory, but not with attention. Our findings suggest a generic mechanism for scene segmentation with the PPC as its anatomical substrate.},
department = {Department Logothetis},
web_url = {http://www.abstractsonline.com/pp8/index.html\#!/4071/presentation/30064},
event_place = {San Diego, CA, USA},
event_name = {46th Annual Meeting of the Society for Neuroscience (Neuroscience 2016)},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Poster { GrassiZB2016_6,
title = {Dynamic bistable Gestalt perception enhances and reduces activity in early visual cortex in retinotopically predicted areas},
year = {2016},
month = {9},
pages = {22},
abstract = {A growing body of literature suggests that feedback modulation of early visual processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content have been shown to suppress early visual regions, typically interpreted in the framework of predictive coding. However, physical stimulus differences can preclude clear interpretations in terms of feedback. Here we examined activity modulation in V1 and V2 during distinct perceptual states associated to the same physical input. This ensures in a unique way that observed signal modulations cannot be accounted for by changes in physical stimulus properties, and can therefore only be accounted for by percept-related feedback interactions from higher level regions. We used a dynamic stimulus consisting of moving dots that could either be perceived as corners of a large moving square (global Gestalt) or as distributed sets of locally moving dots. We found that perceptual binding
of local moving elements into an illusory Gestalt led to spatially segregated differential modulations, in both, V1 and V2: representations of illusory lines and foreground were enhanced, while inducers and background suppressed. The results extend prior findings to the illusory-perceptual state of physically un-changed stimuli, and for the first time show background suppression in the human brain. Based on prior work, we hypothesize that parietal cortex is responsible for the modulations through recurrent connections in a predictive coding account of visual processing.},
department = {Department Logothetis},
web_url = {https://sites.google.com/site/nenaconference/nena-2016},
event_place = {Schramberg, Germany},
event_name = {17th Conference of Junior Neuroscientists of T{\"u}bingen (NeNa 2016): Neuroscience \& Law},
author = {Grassi, P and Zaretskaya, N and Bartels, A}
}
@Poster { GrassiZB2016_2,
title = {Differential modulation of foreground and background in early visual cortex by feedback during bistable Gestalt perception},
journal = {Perception},
year = {2016},
month = {8},
day = {30},
volume = {45},
number = {ECVP Abstract Supplement},
pages = {155},
abstract = {A growing body of literature suggests that feedback modulation of early processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content have been shown to suppress early visual regions, typically interpreted in the framework of predictive coding.
However, physical stimulus differences can preclude clear interpretations in terms of feedback. Here we examined activity modulation in V1-V2 during distinct perceptual states associated to the same physical input. This ensures that observed modulations cannot be accounted for by changes
in physical stimulus properties, and can therefore only be due to percept-related feedback from higher-level regions. We used a bistable dynamic stimulus that could either be perceived as a large illusory square or as locally moving dots. We found that perceptual binding of local elements into an illusory Gestalt led to spatially segregated modulations: retinotopic representations of illusory
contours and foreground were enhanced, while inducers and background suppressed. The results extend prior findings to the illusory-perceptual state of physically unchanged stimuli, and show also percept-driven background suppression in the human brain. Based on our prior work, we
hypothesize that parietal cortex is responsible for the modulations through recurrent connections in a predictive coding account of visual processing.},
department = {Department Logothetis},
web_url = {http://journals.sagepub.com/doi/full/10.1177/0301006616671273},
event_place = {Barcelona, Spain},
event_name = {39th European Conference on Visual Perception (ECVP 2016)},
DOI = {10.1177/0301006616671273},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Poster { ZaretskayaP2016,
title = {Partial Fourier imaging anisotropically reduces spatial independence of BOLD signal time courses},
year = {2016},
month = {6},
day = {28},
number = {1609},
abstract = {Introduction:
Partial Fourier (pF) imaging is a common method used to accelerate image acquisition or shorten the minimum TE in 2D EPI. The technique takes advantage of conjugate symmetry in k-space, which allows acquiring a subset (at least half) of k-space and estimates the skipped data from the acquired data [1], [2]. Despite its wide use for BOLD fMRI and the theoretically predicted blurring effects, the actual impact of pF on spatial independence of the BOLD signal time courses-and hence on the spatial resolution of fMRI experiments-is not known. In this study we quantify the effect of pF on temporal correlation of resting-state BOLD signal time courses along each of the three image encoding dimensions. We find that with increasing pF spatial correlations between neighboring voxels increase anisotropically, with most blurring occurring along the phase-encoding direction.
Methods:
Resting-state BOLD fMRI data were acquired from four healthy volunteers on a Siemens TIM Trio 3T MR scanner using a 32-channel head coil and either a GE (TR=3.3 s, TE=30 ms, FA=90\(^{\circ}\), 2.5 mm3 resolution, 48 axial slices with A–P phase encoding, 120 volumes per measurement) or SE (same parameters as GE but 30 slices and TE=70ms) single-shot 2D EPI sequence. The partial Fourier factor was varied from run to run between 8/8 (i.e. no pF) to 5/8 in a pseudorandom order to avoid confounding effects of fatigue, motion, etc. EPI data were reconstructed using zero-padding algorithm [3].
After standard preprocessing we employed an analysis procedure illustrated in Fig. 1. This procedure generated three maps representing the amount of local temporal correlation along phase-encoding, readout, and slice dimensions. The resulting values were then averaged across all voxels within the brain to yield one global value per run.
To rule out effects of brain tissue asymmetry or physiological noise correlations along different dimensions we conducted separate measurements where the EPI matrix was rotated by ±30\(^{\circ}\) relative to the A–P axis. To exclude the effect of a specific image reconstruction algorithm used, we compared the results obtained using default zero-filling reconstruction with those obtained using the POCS algorithm [4].
Results:
We observed the expected tSNR increase with increasing pF due to implicit spatial smoothing caused by omitting the high spatial frequencies and interpolation during image reconstruction (Fig. 2). The only exception was observed for pF 5/8 in GE sequence, presumably because the signal loss due to strong dephasing (as the echo becomes closer to the edge of the acquisition window) outweighs the smoothing effect.
Importantly, we also observed an anisotropic increase in temporal signal correlation in neighboring voxels, with strongest increase occurring along the phase-encoding dimension (again with an exception of pF 5/8; see Fig. 3A). The observed effect of pF is similar to applying a 1D Gaussian smoothing kernel along the same dimension (Fig. 3B), where pF 6/8 is roughly equivalent to a smoothing of 1.1 mm FWHM (as determined by linear interpolation of the results in Fig. 3B).
Additional control experiments show that the correlation anisotropy is unlikely to be due to differences in tissue or noise properties along different dimensions (Fig. 4A) or the specific reconstruction algorithm used (4B).
Conclusions:
Using partial Fourier for fMRI introduces an asymmetric loss of resolution along the phase-encoding dimension comparable to the effect of smoothing single volumes with a 1D Gaussian kernel during standard preprocessing. This can not only cause bias in high-resolution fMRI analyses where explicit smoothing is avoided [5], but also can complicate interpretation of resting-state functional connectivity including promising new measures of local connectivity anisotropy [6]. This effect is expected to increase with field strength since increases in B0 inhomogeneity cause assumptions of conjugate symmetry and smoothly-varying phase in the image domain to be less justified.},
web_url = {https://ww5.aievolution.com/hbm1601/index.cfm?do=abs.viewAbs\&abs=1486},
event_place = {Geneva, Switzerland},
event_name = {22nd Annual Meeting of the Organization for Human Brain Mapping (OHBM 2016)},
author = {Zaretskaya, N and Polimeni, J}
}
@Poster { GrassiZb2015,
title = {Parietal cortex mediates perceptual Gestalt grouping independent of stimulus size},
year = {2015},
month = {11},
day = {23},
volume = {43},
abstract = {The integration of local moving elements into a unified Gestalt percept has previously been linked to the posterior parietal cortex. There are two possible interpretations
for the lack of involvement of other occipital regions. The first is that parietal cortex is indeed uniquely functionally specialized to perform grouping. Another possibility is that other visual regions can perform grouping as well, but that the large spatial separation of the local elements used previously exceeded their neurons' receptive field (RF) sizes, preventing their involvement. In this study we distinguished between these two alternatives. We measured whole-brain activity using fMRI in response to a bistable motion illusion that induced mutually exclusive percepts of either an illusory global
Gestalt or of local elements. The stimulus was presented in two sizes, a large version known to activate IPS only, and a version sufficiently small to fit into the RFs of mid-level dorsal regions such as V5/MT. We found that none of the separately localized motion regions apart from parietal cortex showed a preference for global Gestalt perception, even for the smaller version of the stimulus. This outcome suggests that grouping is mediated by a specialized size-invariant mechanism with parietal cortex as its anatomical substrate.},
url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/2015/NeNa-2015-Abstract-Book.pdf},
department = {Department Logothetis},
web_url = {https://sites.google.com/site/nenaconference/home},
event_place = {Schramberg, Germany},
event_name = {16th Conference of Junior Neuroscientists of T{\"u}bingen (NeNa 2015): Communicating the Challenges of Science},
author = {Grassi, P and Zaretskaya, N and Bartels, A}
}
@Poster { ZaretskayaFRRP2015,
title = {Characterization of cortical surface reconstruction for
sub-millimeter 7T MPRAGE using FreeSurfer},
year = {2015},
month = {6},
day = {18},
number = {4029},
web_url = {http://www.humanbrainmapping.org/i4a/pages/index.cfm?pageID=3625},
event_place = {Honolulu, HI, USA},
event_name = {21st Annual Meeting of the Organization for Human Brain Mapping (OHBM 2015)},
author = {Zaretskaya, N and Fischl, B and Reuter, M and Renvall, V and Polimeni, J}
}
@Poster { ZaretskayaAB2012_2,
title = {Parietal cortex mediates perceptual grouping across space},
year = {2012},
month = {11},
pages = {57},
abstract = {One of the key real-world challenges to our visual system is posed by cluttered scenes and occluded objects. To make sense of such scenes, local elements belonging to the same object need to be perceptually grouped, also referred to as
spatial binding problem. However, it remains unknown how and where in the brain the local information is grouped together to give rise to a holistic percept. In the
current study we addressed this question with a novel bistable motion stimulus developed by Anstis and Kim (2011) that consists of four pairs of dots coherently moving on a circular path. The stimulus causes perception to alternate spontaneously between two interpretations: local dot motion and global motion of two imaginary squares. Using functional magnetic resonance imaging (fMRI), we found that activity in the right parietal cortex correlated specifically with global as compared to local perception periods. To test for a causal role of parietal function in perceptual grouping, we used transcranial magnetic stimulation (TMS) to temporarily disrupt activity in two subregions of the parietal cortex. TMS over one of the subregions - the right anterior intraparietal sulcus (IPS) - specifically affected the global percept durations without affecting the local ones. Our results provide causal evidence that IPS may play a crucial role in perceptual grouping of local elements into a holistic
percept, suggesting it to be a common anatomical locus of attention, perceptual grouping and perceptual selection processes.},
department = {Department Logothetis},
web_url = {http://www.danielabalslev.dk/workshop/Abstract_booklet.pdf},
event_place = {T{\"u}bingen, Germany},
event_name = {ERNI-HSF Science Meeting: Orienting of Attention: Neural Implementation, Underlying Mechanisms and Clinical Implications},
author = {Zaretskaya, N and Anstis, S and Bartels, A}
}
@Poster { ZaretskayaB2012,
title = {Conscious perception of global motion is related to higher-level motion regions},
year = {2012},
month = {10},
day = {16},
volume = {42},
number = {672.18},
abstract = {The processing of motion in the primate brain is distributed across multiple regions of the cerebral cortex. The two well-studied visual areas MT and MST have been linked to conscious perception and decision-making related to simple flow stimuli as well as to integration of component plaid motion into a coherently moving pattern. However, it is unclear whether processing and perception of other types of global motion, which require large-scale integration of the local signals, is related to activity of the same areas.
In the current study we used fMRI to investigate neural responses to a bi-stable visual motion stimulus. The stimulus consisted of four pairs of dots, each pair coherently moving on a circular path. Perception alternated spontaneously between two states: local dot motion in each of the four quadrants of the visual field or global planar motion of two illusory squares spanning all four visual quadrants [1]. Importantly, these alternations were purely perceptual and involved no stimulus manipulation. We localized visual areas that are known to respond to visual movement (V3a, V6, V7, MT, MST, IPS1-4, and the recently described cingulate sulcus visual area (CSv) [2,3]) individually in each subject. We then investigated responses of these areas to global and local perceptual states of our subjects, while they viewed the bistable stimulus and reported their perception.
We found that activity of two of the areas, CSv and IPS4, specifically correlated with global, but not the local perceptual states, while V6 showed a trend in the opposite direction. Interestingly, neither V5/MT, nor MST, nor any other motion-responsive region differentiated between global and local perceptual states.
Our results suggest that CSv and IPS4 may be involved in the computation of global motion by large-scale integration of similar motion directions, or by spatial binding between distant loci in the visual field, respectively. Importantly, these results imply a certain 'blindness' of V5/MT and of MST to vivid changes in the conscious perception of large-scale motion stimuli. The perception of global, large-scale motion may therefore be mediated by higher-level motion-processing regions with larger receptive fields, such as by areas CSv and IPS4.},
department = {Department Logothetis},
web_url = {http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=7764a0cc-8b09-401e-b3fa-a74ce61fb559\&cKey=f7d13c88-f677-42d2-971b-2e2341868c80\&mKey=70007181-01c9-4de9-a0a2-eebfa14cd9f1},
event_place = {New Orleans, LA, USA},
event_name = {42nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012)},
author = {Zaretskaya, N and Bartels, A}
}
@Poster { ZaretskayaB2012_2,
title = {The Contribution of area V5+/hMT+ to the awareness of motion during binocular rivalry},
year = {2012},
month = {6},
number = {975},
abstract = {Introduction:
Certain areas of the brain are known to be specialized for processing distinct stimulus types. For example, area V5/MT is crucial for processing and perception of visual motion, and regions in the fusiform gyrus (e.g. FFA) are important for processing and perception of faces. When a face is presented to one eye, and visual motion to the other, conscious perception alternates between the two in a random sequence, such that only one of the two is perceived and the other suppressed (a process termed binocular rivalry). It is an unresolved question whether and how activity in the distinct regions specialized for the stimuli contributes to conscious perception during rivalry. It is known however that stimulus-specific responses in these areas can be observed even when subjects are not aware of the stimulus.
Methods:
In the current study we investigated the role of motion-processing area V5/MT+ in the awareness of motion and of faces during binocular rivalry. We interfered with ongoing neural activity in V5+/MT+ by means of transcranial magnetic stimulation (TMS) in 12 human subjects while they reported their perceptual alternations between visual motion and a static face stimulus, each presented to a different eye.
Results:
We found that compared to a control condition in which a neutral site (vertex) was stimulated using TMS, the stimulation of V5+/MT+ did not affect the duration of motion perception periods, but instead lengthened the phases during which the face was perceived (and motion suppressed).
Conclusions:
The observed effect is equivalent to that when the stimulus-strength of one of the two competing stimuli, in this case visual motion, is weakened (e.g. by reducing contrast, luminance or motion speed) (Levelt, 1966). Our findings suggest that activity in V5+/MT+ contributes to the on-going competition for perceptual dominance in binocular rivalry, and that injecting noise into it has effects similar to those of reducing the stimulus strength of the visual motion display. To our knowledge this is the first direct manipulation of activity in a functionally specialized visual area with consequences on conscious perception during binocular rivalry.},
department = {Department Logothetis},
web_url = {http://www.humanbrainmapping.org/i4a/pages/index.cfm?pageid=3458},
event_place = {Beijing, China},
event_name = {18th Annual Meeting of the Organization for Human Brain Mapping (OHBM 2012)},
author = {Zaretskaya, N and Bartels, A}
}
@Poster { ZaretskayaB2011,
title = {Parietal cortex mediates perceptual grouping across space: Evidence from fMRI and TMS},
year = {2011},
month = {11},
volume = {41},
number = {800.14},
abstract = {One of the key real-world challenges to our visual system is posed by cluttered scenes and occluded objects. To make sense of such scenes, local elements belonging to the same object need to be perceptually grouped, also referred to as spatial binding problem. However, it remains unknown how and where in the brain the local information is grouped together to give rise to a holistic percept. In the current study we addressed this question with a novel bistable motion stimulus developed by Anstis and Kim (2011) that consists of four pairs of dots coherently moving on a circular path. The stimulus causes perception to alternate spontaneously between two interpretations: local dot motion and global motion of two imaginary squares. Using functional magnetic resonance imaging (fMRI), we found that activity in the right parietal cortex correlated specifically with global as compared to local perception periods. To test for a causal role of parietal function in perceptual grouping, we used transcranial magnetic stimulation (TMS) to temporarily disrupt activity in two subregions of the parietal cortex. TMS over one of the subregions - the right anterior intraparietal sulcus (IPS) - specifically affected the global percept durations without affecting the local ones. Our results provide causal evidence that IPS may play a crucial role in perceptual grouping of local elements into a holistic percept, suggesting it to be a common anatomical locus of attention, perceptual grouping and perceptual selection processes.},
department = {Department Logothetis},
department2 = {Department Scheffler},
web_url = {http://www.sfn.org/AM2011/},
event_place = {Washington, DC, USA},
event_name = {41st Annual Meeting of the Society for Neuroscience (Neuroscience 2011)},
author = {Zaretskaya, N and Bartels, A}
}
@Poster { ZaretskayaAB2011,
title = {Parietal cortex mediates perceptual grouping of local elements into a whole},
year = {2011},
month = {10},
volume = {12},
pages = {53},
abstract = {Grouping local elements into a holistic percept, also known as spatial binding, is crucial for
meaningful perception. Lesions in posterior parts of the brain are known to impair perceptual
grouping, but in the healthy brain this process has only been studied indirectly. Here we use
a novel bi-stable illusion, which induces alternating and mutually exclusive subjective experiences
of either grouped (global) or ungrouped (local) elements, while the visual stimulation
remains the same. We show that global perceptual periods are related to stronger brain activity
in the parietal cortex and that they are selectively shortened when parietal activity is
disturbed by brain stimulation. Our findings thus provide direct evidence that consciously
experienced grouping is mediated by parietal function, similar to attention and perceptual
selection.},
department = {Department Logothetis},
department2 = {Department Scheffler},
event_place = {Heiligkreuztal, Germany},
event_name = {12th Conference of Junior Neuroscientists of T{\"u}bingen (NeNA 2011)},
author = {Zaretskaya, N and Anstis, S and Bartels, A}
}
@Poster { ZaretskayaTLB2010,
title = {Binocular Rivalry: a Causal role of the Parietal Cortex in Perceptual Selection},
year = {2010},
month = {6},
volume = {16},
number = {145 MT-AM},
pages = {8},
department = {Department Logothetis},
department2 = {Department Scheffler},
web_url = {http://www.humanbrainmapping.org/i4a/pages/index.cfm?pageid=1},
event_place = {Barcelona, Spain},
event_name = {16th Annual Meeting of the Organisation for Human Brain Mapping (HBM 2010)},
author = {Zaretskaya, N and Thielscher, A and Logothetis, NK and Bartels, A}
}
@Conference { GrassiZB2016_3,
title = {Differential modulation of foreground and background in early visual cortex by feedback during bistable Gestalt perception},
year = {2016},
month = {6},
pages = {76-77},
abstract = {A growing body of literature suggests that feedback modulation of early visual processing is ubiquitous and central to cortical computation. In particular stimuli with high-level content have been shown to suppress early visual regions, typically interpreted in the framework of predictive coding. However, physical stimulus differences can preclude clear interpretations in terms of feedback.
Here we examined activity modulation in the early visual
cortex (V1 and V2) using fMRI during distinct perceptual states associated to the same physical input. This ensures in a unique way that observed signal modulations cannot be accounted for by changes in physical stimulus properties, and can therefore only be accounted for by percept-related feedback interactions from higher level regions. We used a dynamic stimulus consisting of moving dots that could either be perceived as corners of a large moving square (global Gestalt) or as distributed sets of locally
moving dots. We found that perceptual binding of local moving elements into an illusory Gestalt led to spatially segregated differential modulations, in both, V1 and V2: retinotopic representations of illusory lines and foreground were enhanced, while inducers and background suppressed. The results extend prior findings to the illusory-perceptual state of physically un-changed
stimuli, and show percept-driven background suppression in the human brain. Based on prior work, we hypothesize that parietal cortex is responsible for the modulations through recurrent connections in a predictive coding account of visual processing.},
department = {Department Logothetis},
talk_type = {Abstract Talk},
web_url = {http://www.neurizons.uni-goettingen.de/wp-content/uploads/Neurizons-booklet_2016.pdf},
event_place = {G{\"o}ttingen, Germany},
event_name = {7th Biennial Neuroscience Conference Neurizons 2016: Speak your mind},
author = {Grassi, PR and Zaretskaya, N and Bartels, A}
}
@Conference { ZaretskayaGSB2016,
title = {Neural bases of bistable perception in the human brain},
year = {2016},
month = {3},
day = {22},
volume = {58},
pages = {383},
abstract = {Ambiguous visual stimuli, and in particular binocular rivalry, provide a great experimental tool to study the neural basis of conscious vision. When viewed continuously, such stimuli cause the perceptual state of the observer to alternate between the two possible interpretations despite
unchanged visual input. A great number of neuroimaging studies linked bi-stable perception to activity in lower-level sensory, but also higher-level attention-related areas of the brain such as parietal and frontal regions. In this talk, we will discuss a series of studies from our lab that used fMRI, TMS and tDCS trying to understand how different brain areas contribute to transforming the constant sensory input into a changing perceptual experience.},
department = {Department Logothetis},
talk_type = {Abstract Talk},
web_url = {https://www.teap.de/memory/Abstractband_58_2016_Heidelberg.pdf},
event_place = {Heidelberg, Germany},
event_name = {58th Conference of Experimental Psychologists (TeaP 2016)},
author = {Zaretskaya, N and Grassi, P and Sipatchin, A and Bartels, A}
}
@Conference { Zaretskaya2013,
title = {Causal contributions of parietal cortex to perceptual selection and spatial binding},
year = {2013},
month = {10},
day = {11},
department = {Department Logothetis},
talk_type = {Invited Lecture},
web_url = {http://www.cin.uni-tuebingen.de/news-events/browse-all-events/detail/view/338/page/1/3rd-nips-cin-joint-symposium.html},
event_place = {Okazaki, Japan},
event_name = {3rd NIPS-CIN Joint Symposium},
author = {Zaretskaya, N}
}
@Conference { 7083,
title = {The effects of TMS over the parietal cortex on binocular rivalry},
year = {2010},
month = {10},
volume = {11},
pages = {14},
abstract = {Human fMRI studies of binocular rivalry and other bistable phenomena suggest that a network of frontal and parietal areas, predominantly in the right hemisphere, is particularly involved during switches between the two conflicting percepts. However, these studies do not provide information about causality, i.e. whether fMRI activity is a consequence or a cause of the perceptual change. In the current study we localized areas that were activated
during perceptual switches in individual subjects using fMRI. We then tested the effect of disturbing neural processing in two distinct parietal regions along the ventral-dorsal axis in both hemispheres using 2 Hz repetitive transcranial magnetic stimulation (TMS). Our results show that on the group level, TMS over the right intraparietal sulcus (IPS) prolonged the periods of stable percepts. In individual subjects, the IPS in the hemisphere with higher fMRI activation also showed a stronger TMS effect, as reflected in the positive correlation between
the lateralization of TMS effects and that of fMRI activations. Our results thus demonstrate a causal, de-stabilizing effect of the IPS on perceptual continuity and provide a direct link between correlational and causal measures of cortical function during conscious perception.},
department = {Department Logothetis},
talk_type = {Abstract Talk},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Heiligkreuztal, Germany},
event_name = {11th Conference of Junior Neuroscientists of T{\"u}bingen (NeNa 2010)},
language = {en},
author = {Zaretskaya, N}
}